DHCP, NAT and Firewall

I've gotten some really good answers to this point on a couple other topics and hope that I can get one more I have looked through the forum answers and have found a few that seem to come close to fitting the bill but nothing dead on. Here is my problem. I am a residential Road Runner customer trying to install zimbra behind a linksys router that's providing NAT for the actual server. Residential Road Runner is DHCP so my IP address resovles to a Road Runner domain. I signed up for, and have to renew, a dyndns account with my own domain and MX record so they seem to work.

My problem is sending AND receiving email at the same time. With DNS check enabled I can send out but can't receive. With DNS check turned off I can receive but can't send. I might have that reversed but the behavior is basically as described. I've tried adding entries into my /etc/hosts file for my dyndns name and local host with various configurations but I can't get send and receive to work at the same time. Is there a tutorial on how to configure this specific setup? Is there something that I am missing or could tweak without getting overly complicated? I don't currently have any experience with DNS servers and would like to avoid setting up an internal server solely for the purpose of "fooling" Zimbra.

;; ADDITIONAL SECTION:
mjolnir.dnsdojo.net. 60 IN A 74.67.179.245
ns1.dyndns.org. 38167 IN A 63.208.196.90
ns2.dyndns.org. 27124 IN A 204.13.249.81
ns3.dyndns.org. 63326 IN A 204.13.250.81
ns4.dyndns.org. 59679 IN A 213.155.150.205
ns5.dyndns.org. 63326 IN A 63.170.10.81

Is there something that I am missing or could tweak without getting overly complicated? I don't currently have any experience with DNS servers and would like to avoid setting up an internal server solely for the purpose of "fooling" Zimbra.

I'm afraid it's time to learn DNS.

It's not a case of 'fooing' Zimbra (actually, it's Postfix that needs the DNS lookup), the problem is your server can't be found via DNS when you're behind a NAT router. The only address a DNS lookuk will see is the public IP assigned to the router, your private LAN IP of 192.168.x.x is 'invisible' to DNS. In order to get over that you'll need a DNS server on your LAN so that when a DNS lookup is made your internal IP will resolve to your ZImbra server and you will be able to send & receive mail happily. There's an introduction to that setup on the wiki, it's split-DNS.

Before you go down that route, there may be one trick you might be able to use if your router has it. Have a look at the documentation or in a linksys forum and see if there's a feature called 'loopback', if it has that then you may be in luck. Let us know if it has.